U.S. patent number 7,435,906 [Application Number 11/509,639] was granted by the patent office on 2008-10-14 for touch panel, transparent conductor and transparent conductive film using the same.
This patent grant is currently assigned to TDK Corporation. Invention is credited to Youichi Kobayashi, Noriyuki Yasuda.
United States Patent |
7,435,906 |
Yasuda , et al. |
October 14, 2008 |
Touch panel, transparent conductor and transparent conductive film
using the same
Abstract
In a transparent conductor containing conductive particles and a
binder, the conductive particles have an average particle size of
60 nm or smaller, and the number of conductive particles having an
average particle size of 100 nm or greater is 10% or less of the
total number of conductive particles.
Inventors: |
Yasuda; Noriyuki (Tokyo,
JP), Kobayashi; Youichi (Tokyo, JP) |
Assignee: |
TDK Corporation (Tokyo,
JP)
|
Family
ID: |
37802787 |
Appl.
No.: |
11/509,639 |
Filed: |
August 25, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
|
US 20070045593 A1 |
Mar 1, 2007 |
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Foreign Application Priority Data
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Aug 31, 2005 [JP] |
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P2005-251478 |
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Current U.S.
Class: |
174/94R;
174/102SC |
Current CPC
Class: |
H01B
1/22 (20130101) |
Current International
Class: |
H01B
1/00 (20060101) |
Field of
Search: |
;174/94R,102SC |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Nguyen; Chau N
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
What is claimed is:
1. A touch panel comprising: a transparent conductive film, wherein
said transparent conductive film comprises a support and a
transparent conductor provided on said support, wherein said
transparent conductor contains conductive particles and a binder,
wherein said conductive particles have an average particle size of
60 nm or smaller, wherein the number of conductive particles having
a particle size of 100 nm or greater is 10% or less of the total
number of conductive particles, and wherein the binder is selected
from the group consisting of acrylic binders, epoxy binders,
polystyrene, polyurethane and fluorine binders.
2. A touch panel according to claim 1, wherein the number of
conductive particles having a particle size of 40 to 80 nm is 50%
or greater of the total number of conductive particles.
3. A touch panel according to claim 2, wherein the average particle
size is 10 nm or greater.
4. A touch panel according to claim 1, wherein the average particle
size is 10 nm or greater.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transparent conductor and a
transparent conductive film using the same.
2. Related Background Art
In general, a panel switch such as touch panel is constructed by a
pair of transparent electrodes opposing each other and a spacer
held between the pair of transparent electrodes. When one of the
transparent electrodes is pushed in such a panel switch, this
transparent electrode comes into contact with the other transparent
electrode, so as to conduct electricity, whereby the position of
the point of contact is detected. Employed as the transparent
electrode is a transparent conductive film, whereas the transparent
conductive film has a transparent conductor in which conductive
particles are dispersed in a binder.
In general, conductive particles are dispersed in such a
transparent conductor. However, in general, each conductive
particle is a secondary particle into which primary particles
flocculate. When light is incident on the transparent conductor,
the conductive particles scatter the light, thereby lowering the
light transmittance and haze value of the transparent conductor.
Therefore, transparent conductors having a sufficient light
transmittance and haze value have been in demand.
As such a transparent conductor, a transparent conductor in which
the volume content of conductive particles is 50 to 80%, for
example, has conventionally been disclosed, and it has been
proposed to improve the light transmittance and haze value by this
transparent conductor (see Japanese Patent No. 3072862). Here,
ultrafine particles of indium tin oxide having an average particle
size of 30 nm are employed as the conductive particles.
SUMMARY OF THE INVENTION
However, the transparent conductive film disclosed in the
above-mentioned Japanese Patent Publication No. 3072862 may fail to
exhibit sufficient light transmittance and haze value, and may be
unsuitable as a film used for panel switches in particular.
In view of the foregoing circumstances, it is an object of the
present invention to provide a transparent conductor which can
reliably realize sufficient light transmittance and haze value, and
a transparent conductive film using the same.
The inventors conducted diligent studies in order to solve the
problems mentioned above and, as a result, found that not only the
average particle size of conductive particles but also their
particle size distribution is important for improving the light
transmittance and haze value. The inventors have further conducted
diligent studies and found that the above-mentioned problems can be
solved when the conductive particles have an average particle size
of a predetermined value or smaller while the ratio of conductive
particles having a predetermined particle size or greater is a
predetermined value or smaller in the particle size distribution of
conductive particles, thereby completing the present invention.
Namely, in one aspect, the present invention provides a transparent
conductor containing conductive particles and a binder, wherein the
conductive particles have an average particle size of 60 nm or
smaller, and wherein the number of conductive particles having an
average particle size of 100 nm or greater is 10% or less of the
total number of conductive particles. Here, the transparent
conductor in the present invention encompasses film- and sheet-like
transparent conductors, in which the film-like transparent
conductors refer to those having a thickness falling within the
range of 50 nm to 1 mm, whereas the sheet-like transparent
conductors refer to those having a thickness exceeding 1 mm.
In this transparent conductor, the average particle size is 60 nm
or smaller, whereas the number of conductive particles having an
average particle size of 100 nm or greater is 10% or less of the
total number of conductive particles, so that the conductive
particles have a small particle size on the whole while the ratio
of conductive particles having a particle size of 100 nm or greater
that become a main cause of light scattering is sufficiently small.
Therefore, light incident on the transparent conductor of the
present invention is sufficiently restrained from scattering. This
can reliably realize sufficient light transmittance and haze
value.
When the average particle size of the conductive particles exceeds
60 nm, sufficient light transmittance and haze value cannot be
realized reliably. When the number of conductive particles having a
particle size of 100 nm or greater exceeds 10% of the total number
of conductive particles, the light transmittance and haze value
decrease remarkably.
Preferably, in the transparent conductor, the number of conductive
particles having a particle size of 40 to 80 nm is 50% or greater
of the total number of conductive particles. In this case, incident
light is further restrained from scattering, whereby the light
transmittance and haze value can be improved more.
Preferably, in the transparent conductor, the conductive particles
have an average particle size of 10 nm or greater. This can more
fully suppress the change in conductivity caused by a reaction of
the conductive particles with oxygen.
In another aspect, the present invention provides a transparent
conductive film comprising a support and the transparent conductor
provided on the support. This transparent conductive film has the
above-mentioned transparent conductor, and thus is excellent in
light transmittance and haze value. Therefore, this transparent
conductive film is favorably used for touch panels and the
like.
The present invention can provide a transparent conductor which can
reliably realize sufficient light transmittance and haze value, and
a transparent conductive film using the same.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic sectional view showing a first embodiment of
the transparent conductive film in accordance with the present
invention;
FIG. 2 is a view for explaining the particle size of a conductive
particle; and
FIG. 3 is a schematic sectional view showing a second embodiment of
the transparent conductive film in accordance with the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following, preferred embodiments of the present invention
will be explained in detail with reference to the drawings as
necessary. In the drawings, the same constituents will be referred
to with the same numerals without repeating their overlapping
descriptions. Ratios of sizes in the drawings are not limited to
those depicted.
[First Embodiment]
FIG. 1 is a schematic sectional view showing a first embodiment of
the transparent conductive film in accordance with the present
invention. As shown in FIG. 1, the transparent conductive film 10
in accordance with this embodiment comprises a support 14 and a
transparent conductor 15 provided on the support 14. The
transparent conductor 15 contains conductive particles 11 and a
binder 12, whereas the transparent conductor 15 is filled with the
conductive particles 11 such that the conductive particles 11
adjacent to each other are in contact with each other. This enables
conduction in the transparent conductor 15.
The transparent conductor 15 will now be explained in further
detail.
Transparent Conductor
The transparent conductor 15 usually contains the conductive
particles 11 and the binder 12.
Conductive Particles
The conductive particles 11 are constructed by a transparent
conductive oxide material. The transparent conductive oxide
material is not restricted in particular as long as it is
transparent and conductive. Examples of the transparent conductive
oxide material include indium oxide; indium oxide doped with at
least one species of elements selected from the group consisting of
tin, zinc, tellurium, silver, gallium, zirconium, hafnium, and
magnesium; tin oxide; tin oxide doped with at least one species of
elements selected from the group consisting of antimony, zinc, and
fluorine; zinc oxide; and zinc oxide doped with at least one
species of elements selected from the group consisting of
aluminium, gallium, indium, boron, fluorine, and manganese.
Preferably, the filling ratio of the conductive particles 11 in the
transparent conductor 15 is 10 vol % to 70 vol %. When the filling
ratio is less than 10 vol %, the electric resistance value of the
transparent conductor 15 tends to become higher than in the case
where the filling ratio falls within the range mentioned above.
When the filling ratio exceeds 70 vol %, the mechanical strength of
the conductive particle 15 tends to decrease as compared with the
case where the filling ratio falls within the range mentioned
above.
Preferably, the conductive particles 11 have a specific surface
area of 10 to 50 m.sup.2/g. When the specific surface area is less
than 10 m.sup.2/g, the scattering of visible light tends to become
greater than in the case where the specific surface area falls
within the range mentioned above. When the specific surface area
exceeds 50 m.sup.2/g, the transparent conductive material tends to
lower its stability as compared with the case where the specific
surface area falls within the range mentioned above. Here, the
specific surface area refers to a value measured by a specific
surface area measuring apparatus (type: NOVA2000 manufactured by
Quantachrome Instruments) after drying a sample in vacuum for 30
minutes at 300.degree. C. However, the object of the present
invention is achievable even when the specific surface area of the
conductive particles 11 is outside of the above-mentioned
range.
The conductive particles 11 have an average particle size of 60 nm
or smaller. Here, the average particle size is a value measured by
using transmission electron microscopy (TEM). Namely, the average
particle size is a value calculated by cutting the transparent
conductor 15, observing 150 conductive particles 11 on the cut
plane, measuring the maximum particle size Lmax in each of the
conductive particles 11 (see FIG. 2), and averaging thus measured
values.
When the average particle size exceeds 60 nm, light scattering
becomes greater than that in the case where the average particle
size falls within the range mentioned above, so that the light
transmittance in the transparent conductor 15 decreases, thereby
increasing the haze value. Preferably, the average particle size is
10 nm or greater. When the average particle size is less than 10
nm, the conductivity of the transparent conductor 15 is more likely
to decrease than in the case where the average particle size falls
within the range mentioned above. Namely, while oxygen defects
occurring in the conductive particles 11 generate conductivity in
the transparent conductor 15 in accordance with this embodiment,
the oxygen defects decrease, for example, when the external oxygen
concentration is high in the case where the average particle size
of the conductive particles 11 is less than 10 nm, whereby the
conductivity may become lower.
In the transparent conductor 15, the number of conductive particles
11 having a particle size of 100 nm or greater is 10% or less of
the total number of conductive particles 11. When this ratio
exceeds 10%, the light transmittance and haze value of the
transparent conductor 15 decrease remarkably.
Preferably, the particle size of the conductive particles 11 is 40
to 80 nm. The lower limit of the particle size is thus set to 40 nm
in order to secure stability in the resistance value of the
transparent conductor, whereas the upper limit is set to 80 nm
since it becomes a threshold at which optical properties (optical
transmission and haze value) greatly change. However, the object of
the present invention is achievable even when the particle size of
the conductive particles 11 is outside of the above-mentioned
range.
The form of the conductive particles 11 is not limited in
particular as long as their average particle size and maximum
particle size fall within the respective ranges mentioned above.
Examples of forms of the conductive particles 11 include spheres,
ellipsoids, and amorphous forms obtained when they are fused
together.
Thus, in the transparent conductor 15 in accordance with this
embodiment, the average particle size is 60 nm or smaller, whereas
the number of conductive particles 11 having a particle size of 100
nm or greater is 10% or less of the total number of conductive
particles 11, so that the conductive particles 11 have a small
particle size on the whole while the ratio of conductive particles
11 having a particle size of 100 nm or greater that become a main
cause of light scattering is sufficiently small. Therefore, light
incident on the transparent conductor 15 of the present embodiment
is sufficiently restrained from scattering. This can reliably
realize sufficient light transmittance and haze value.
The average particle size and particle size distribution of the
conductive particles 11 can be adjusted in the following manner.
Namely, raw materials for the conductive particles 11 are
pulverized in a pulverizer such as homomixer, bead mill, ball mill,
colloid mill, air flow pulverizer, medialess mill, or ultrasonic
disperser, whereby the average particle size and particle size
distribution can be adjusted.
Preferably, a bead mill pulverizer which pulverizes conductive
particles in a liquid is used as the pulverizer. In this case, the
range of particle size distribution in the resulting conductive
particles can be made narrower.
Preferably, the beads used in the bead mill pulverizer have a
diameter of 15 to 50 .mu.m. This can yield conductive particles
having a smaller average particle size.
When the conductive particles include those having a greater
particle size after the pulverization mentioned above, the
conductive particles having a greater particle size may be
separated by centrifugation, electrophoresis, filtration, or the
like.
When performing centrifugation, for example, conductive particles
having a predetermined particle size can be separated by adjusting
the number and time of rotations of a centrifuge, whereby the
average particle size and particle size distribution of conductive
particles can be regulated. When performing electrophoresis, the
average particle size and particle size distribution can be
regulated by adjusting current, time, and the like. When performing
filtration, the average particle size and particle size
distribution can be regulated by adjusting the pore size of a
filter employed.
Binder
The binder 12 is not limited in particular as long as it can secure
the conductive particles 11. Examples of the binder 12 include
acrylic binders, epoxy binders, polystyrene, polyurethane, silicone
binders, and fluorine binders.
Among them, acrylic binders are preferably used as the binder 12.
This can improve the light transmittance of the transparent
conductive film 10 more. Namely, the transparent conductive film 10
containing an acrylic binder as the binder 12 can improve its
transparency more. Acrylic binders are also excellent in chemical
resistances to acids and alkalis and scratch resistance (surface
hardness). Therefore, the transparent conductive film 10 containing
an acrylic binder in the transparent conductor 15 is more favorably
used in a touch panel or the like which is supposed to be wiped
with a wiping agent containing an organic solvent, a surfactant, or
the like or have the surface 10a coming into contact with or be
rubbed against the surface 10a of its opposing transparent
conductor 15.
The binder 12 is manufactured by polymerizing a radically
polymerizable compound, an ionically polymerizable compound, or a
thermally polymerizable compound. The radically polymerizable
compound refers to an organic compound which is polymerized by a
radical. The ionically polymerizable compound refers to an organic
compound which is polymerized by a cation. The thermally
polymerizable compound refers to an organic compound which is
polymerized by heat. These organic compounds contain a substance to
become a raw material for the binder 12. Specifically, they contain
monomers, dimers, trimers, oligomers, and the like which can form
the binder 12.
Among them, monomers of a radically polymerizable compound or
monomers of an ionically polymerizable compound are used
preferably. This is advantageous in that the process management
becomes easier, since the polymerization reaction can be
controlled, while polymerization can be achieved in a short time.
More preferably, among the monomers mentioned above, monomers of a
radically polymerizable compound are used. This is advantageous in
that the reproducibility in film thickness and the dimensional
precision in the transparent conductor 15 are easier to attain than
in the case of ionic polymerization of the monomers of the
ionically polymerizable compound, since the monomers of the
radically polymerizable compound are polymerized together
instantaneously upon irradiation with light. It will be sufficient
if such monomers of the radically polymerizable compounds contain a
vinyl group or its derivatives. Their specific examples include
acrylic acid and its derivatives, methacrylic acid and its
derivatives, and styrene and its derivatives. They may be used
singly or in mixtures of two or more species.
Preferably, the refractive index of the transparent conductor 15 is
1.5 or less. When the refractive index is less than 1.5, the
reflectance decreases more than in the case where the refractive
index is 1.5 or greater, whereby transparency tends to improve
more.
Preferably, the thickness of the transparent conductor 15 is 0.1 to
5 .mu.m. When the thickness is less than 0.1 .mu.m, the resistance
value tends to be harder to stabilize than in the case where the
thickness falls within the range mentioned above. When the
thickness exceeds 5 .mu.m, the transparency tends to decrease more
than in the case where the thickness falls within the range
mentioned above. However, the object of the present invention is
achievable even when the thickness of the transparent conductor 15
is outside of the above-mentioned range.
Preferably, the transparent conductor 15 has a Tg of 30.degree. C.
or higher. The Tg of 30.degree. C. or higher can maintain the
morphology of the transparent conductor 15 even when the latter is
used for a long period.
Support
The transparent conductive film 10 of this embodiment is provided
with the support 14. The support 14 is not limited in particular as
long as it is constructed by a material transparent to high-energy
lines which will be explained later and visible light. Namely, the
support 14 may be a known transparent film. Examples of such a
transparent film include films of polyesters such as polyethylene
terephthalate (PET), films of polyolefins such as polyethylene and
polypropylene, polycarbonate films, acrylic films, and norbornene
films (e.g., ARTON manufactured by JSR Corporation). Not only the
resin films, but glass may also be used as the support 14.
Preferably, the support 14 is made of a resin alone. This makes the
transparent conductive film 10 better in transparency and
bendability than in the case where the support 14 contains a resin
and other components. Therefore, the transparent conductive film 10
using the support 14 made of a resin alone is effective in
particular for use in panel switches such as touch panels, for
example.
Intermediate layers may further be provided between the support 14
and transparent conductor 15. The number of intermediate layers is
not limited in particular, whereas they may be provided as
necessary. Examples of the intermediate layers include layers
functioning as buffer layer, conductive auxiliary layer, dispersion
prevention layer, UV-blocking layer, coloring layer, and polarizing
layer. Preferably, these layers are constructed by a resin, an
inorganic oxide, or their composite.
The transparent conductive film 10 in accordance with this
embodiment has the transparent conductor 15, and thus can reliably
realize sufficient light transmittance and haze value.
Manufacturing Method
A method of manufacturing the transparent conductive film 10 in
accordance with this embodiment in the case using tin-doped indium
oxide (hereinafter referred to as "ITO") as the above-mentioned
conductive particles 11 will now be explained.
To begin with, a support 14 is mounted on a glass substrate which
is not depicted, and a transparent conductor 15 containing
conductive particles 11 and a binder 12 is formed on the support
14. A method of manufacturing the conductive particles 11 will now
be explained.
First, indium chloride and tin chloride are coprecipitated by
neutralization with an alkali (precipitating step). Here, the salt
yielded as a byproduct is eliminated by decantation or
centrifugation. Thus obtained coprecipitate is dried, and the
resulting dried product is fired in an atmosphere and pulverized.
This manufactures conductive particles. It will be preferred from
the viewpoint of controlling oxygen defects if the firing is
performed in a nitrogen atmosphere or in an atmosphere of a rare
gas such as helium, argon, or xenon.
Thus obtained conductive particles are dispersed into water, and a
bead mill pulverizer, for example, is used such that the average
particle size is 60 nm or smaller, while the number of conductive
particles having a particle size of 100 nm or greater is 10% or
less of the total number of conductive particles. If necessary, the
conductive particles may be subjected to filtering. Then, thus
obtained conductive particles 11 and the binder 12 are mixed
together and dispersed into a liquid, so as to yield a dispersion
liquid. Examples of the liquid for dispersing the conductive
particles 11 and binder 12 include saturated hydrocarbons such as
hexane; aromatic hydrocarbons such as toluene and xylene; alcohols
such as methanol, ethanol, propanol, and butanol; ketones such as
acetone, methylethylketone, isobutylmethylketone, and
diisobutylketone; esters such as ethyl acetate and butyl acetate;
ethers such as tetrahydrofuran, dioxane, and diethyl ether; and
amides such as N,N-dimethylacetamide, N,N-dimethylformamide, and
N-methylpyrrolidone. The binder 12 may be dissolved in the
above-mentioned liquid beforehand, and then the conductive
particles 11 may be mixed into this liquid, so as to yield a
dispersion liquid.
Subsequently, thus obtained dispersion liquid is applied onto the
support 14. The support 14 can be provided beforehand with an
anchor layer on the surface side to attach the transparent
conductor 15. Providing the anchor layer beforehand on the support
14 can fix the transparent conductor 15 through the anchor layer on
the support 14 more firmly. Polyurethane or the like is favorably
used as the anchor layer.
Preferably, after being applied by coating, the dispersion liquid
is dried, so as to yield an unpolymerized transparent conductor.
Examples of the coating method include reverse rolling, direct
rolling, blading, knifing, extrusion, nozzle method, curtaining,
gravure rolling, bar coating, dipping, kiss coating, spin coating,
squeezing, and spraying.
Then, the unpolymerized transparent conductor provided on the
support 14 is polymerized. When the unpolymerized conductive layer
contains a radically polymerizable component, this component is
polymerized upon irradiation with high-energy lines, whereby the
transparent conductor 15 is formed. When the unpolymerized
transparent conductor contains an ionically polymerizable
component, this component is polymerized by adding a cationic
polymerization initiator thereto, whereby the transparent conductor
15 is formed. When the unpolymerized transparent conductor contains
a thermally polymerizable component, this component is polymerized
by heating, whereby the transparent conductor 15 is formed. The
above-mentioned high-energy lines may be not only UV rays, but also
electron beams, .gamma.-rays, x-rays, and the like as long as they
can generate a radical.
Thus, the transparent conductor 15 is formed on one surface of the
support 14, whereby the transparent conductive film 10 shown in
FIG. 1 is obtained. This transparent conductive film 10 is
favorably used for panel switches such as touch panels and
light-transmitting switches. For example, the transparent
conductive film 10 is used as at least one of transparent
electrodes in a touch panel comprising a pair of transparent
electrodes opposing each other and a dot spacer held between the
transparent electrodes. The transparent conductive film 10 is
favorably usable in not only the panel switches but also antinoise
components, heating elements, electrodes for EL, electrodes for
backlight, LCD, PDP, and the like.
[Second Embodiment]
A second embodiment of the transparent conductor in accordance with
the present invention will now be explained. Constituents identical
or equivalent to those in the first embodiment will be referred to
with numerals identical thereto without repeating their overlapping
descriptions.
FIG. 3 is a sectional view showing the second embodiment of the
transparent conductive film in accordance with the present
invention. As shown in FIG. 3, the transparent conductive film 20
in accordance with this embodiment differs from the transparent
conductive film 10 in accordance with the first embodiment in that
it further comprises a binder layer 13 between the support 14 and
transparent conductor 15. The binder layer 13 in accordance with
the second embodiment is constructed by the above-mentioned binder
12.
Preferably, the refractive index of the binder layer 13 is 1.5 or
less. When the refractive index is less than 1.5, the reflectance
decreases more than in the case where the refractive index is 1.5
or greater, whereby transparency tends to improve.
Preferably, the thickness of the binder layer 13 is 0.1 to 5 .mu.m.
When the thickness is less than 0.1 .mu.m, the electric resistance
value tends to be harder to stabilize than in the case where the
thickness falls within the range mentioned above. When the
thickness exceeds 5 .mu.m, the transparency tends to decrease more
than in the case where the thickness falls within the range
mentioned above. However, the object of the present invention is
achievable even when the thickness of the binder layer 13 is
outside of the above-mentioned range.
Manufacturing Method
A method of manufacturing the transparent conductive film 20 in
accordance with this embodiment will now be explained.
First, conductive particles 11 are mounted on a glass substrate
which is not depicted. Preferably, an anchor layer for securing the
conductive particles 11 onto the substrate is provided on the
substrate beforehand. When the anchor layer is provided beforehand,
the conductive particles 11 can firmly be secured onto the
substrate. The conductive particles 11 can be mounted easily. For
example, polyurethane or the like is favorably used as the anchor
layer.
For securing the conductive particles 11 onto the substrate, it
will be preferred if the conductive particles 11 are compressed
toward the substrate, so as to form a compressed layer. This is
useful in that the conductive particles 11 can be attached to the
substrate without forming the anchor layer. The compression can be
effected by sheet pressing, roll pressing, and the like. It will
also be preferred in this case if an anchor layer is provided
beforehand on the substrate. This allows the conductive particles
11 to be secured more firmly. Not only glass, but films of
polyester, polyethylene, and polypropylene, and various plastic
supports, for example, are also usable as the substrate.
After thus forming the compressed layer of conductive particles 11
on the substrate, a transparent conductor 15 and a binder layer 13
are formed. As the binder 12, one curable by high-energy lines
which will be explained later is used. When the binder 12 has such
a high viscosity that it is hard to process, when the binder 12 is
solid, and the like, the binder 12 is dispersed into a liquid, so
as to form a dispersion liquid. Examples of the liquid for
dispersing the binder 12 include saturated hydrocarbons such as
hexane; aromatic hydrocarbons such as toluene and xylene; alcohols
such as methanol, ethanol, propanol, and butanol; ketones such as
acetone, methylethylketone, isobutylmethylketone, and
diisobutylketone; esters such as ethyl acetate and butyl acetate;
ethers such as tetrahydrofuran, dioxane, and diethyl ether; and
amides such as N,N-dimethylacetamide, N,N-dimethylformamide, and
N-methylpyrrolidone. The binder 12 may be dissolved in the liquid
instead of being dispersed therein. Fillers and crosslinking agents
may be added to the binder 12.
The binder 12 or the dispersion liquid of the binder 12 is applied
by coating onto one surface of the compressed layer. Then, a part
of the binder 12 infiltrates the compressed layer. Preferably,
after coating, the dispersion liquid is subjected to a drying
process. Examples of the coating method include reverse rolling,
direct rolling, blading, knifing, extrusion, nozzle method,
curtaining, gravure rolling, bar coating, dipping, kiss coating,
spin coating, squeezing, and spraying.
Subsequently, a support 14 is attached onto the binder 12. The
support 14 may be provided beforehand with an anchor layer on the
surface to be attached to the binder 12. Providing the anchor layer
beforehand on the support 14 allows the binder 12 to be fixed more
firmly onto the support 14 through the anchor layer. Polyurethane
and the like are favorably used as the anchor layer.
Next, high-energy lines are emitted from above the support 14
provided on the binder 12, so as to cure the binder 12 and a part
of the binder 12 infiltrated in the compressed layer, thereby
forming the transparent conductor 15 and binder layer 13. When a
thermoplastic resin is used as a part of the binder 12 infiltrated
in the compressed layer, it is cured by heating. Examples of the
high-energy lines include UV rays, electron beams, .gamma.-rays,
and x-rays.
Subsequently, the substrate is peeled off from the transparent
conductor 15, whereby the transparent conductor 15 and binder layer
13 are formed on one surface of the support 14. Thus, the
transparent conductive film 20 shown in FIG. 3 is obtained.
Though preferred embodiments of the present invention are explained
in the foregoing, the present invention is not limited to the
above-mentioned embodiments.
The transparent conductor 15 in the first and second embodiments
may contain the following optional components.
Optional Components
Fluorine Coating Agent
The transparent conductor 15 may contain a fluorine coating agent
including a fluorine compound, whereas a surface 10a of the
transparent conductor 15 may be coated with a fluorine coating
agent.
In this case, since the fluorine coating agent includes a fluorine
compound, the difference between refractive indexes of air and the
transparent conductor 15 becomes smaller. Even when the transparent
conductors 15 rub against each other, the surfaces of the
transparent conductors 15 can be prevented from being shaved.
Further, the transparent conductors shaved thereby can be prevented
from attaching again, whereby the transparent conductor 15 adapted
to suppress the fluctuation in electric resistance value can be
obtained.
The fluorine compound is not limited in particular as long as it
includes at least one fluorine atom in its molecule. Specific
examples include perfluoropolyethers and their derivatives,
fluorine-containing alcohols such as 2-perfluorodecylethanol,
fluorine-containing acid halides such as perfluorooctanoyl
fluoride, fluorine-containing acids such as perfluorodecanoic acid,
fluorine-containing acrylates such as 2-(perfluorooctyl)ethyl
acrylate, fluorine-containing methacrylates such as
2-(perfluoro-5-methylhexyl) ethyl methacrylate,
perfluoro(2,5,8,11-tetramethyl-3,6,9,12-tetraoxapentadecanoyl)
fluoride, perfluoropolyoxetanes and their derivatives,
3-perfluorohexyl-1,2-epoxypropane,
di-heptadecatrifluorodecyldisilazane,
heptadecatrifluorodecyltrimethoxysilane, and 1H,
1H-heptadecafluorononylamine. They may be used either singly or in
mixtures of two or more species.
Preferably, the molecular weight of the fluorine compound is 200 to
20,000. When the molecular weight is less than 200, lubricity tends
to become lower than in the case where the molecular weight falls
within the range mentioned above. When the molecular weight exceeds
20,000, the electric resistance value tends to rise more than in
the case where the molecular weight falls within the range
mentioned above.
Preferably, the compounding amount of the fluorine compound is 5 to
70 parts by mass with respect to 100 parts by mass in total of the
transparent conductor 15 and fluorine compound. When the
compounding amount is less than 5 parts by mass, the effect of
adding the fluorine compound is less likely to achieve than in the
case where the compounding amount falls within the range mentioned
above. When the compounding amount exceeds 70 parts by mass, the
resistance value tends to increase more than in the case where the
compounding amount falls within the range mentioned above.
Conductive Comipound
The transparent conductor 15 may contain a conductive compound.
Specifically, it will be preferred if the conductive compound is
constructed by at least one species of conductive polymer selected
from the group consisting of polyacetylene, polypyrrole,
polythiophene, polyphenylenevinylene, polyphenylene, polysilane,
polyfluorene, and polyaniline, or at least one species of carbon
material selected from the group consisting of activated carbon,
carbon blacks such as acetylene black and Ketjenblack, graphite,
carbon fired at low temperature, carbon easier to graphitize,
carbon harder to graphitize, and carbon nanotubes.
When the conductive compound is the above-mentioned conductive
polymer or carbon material, the electric compensation by these
materials can be made more reliable. Namely, even when the distance
between the conductive particles becomes wider, the resistance
value can be prevented from changing. Therefore, in this case, the
rise and temporal change in electric resistance value in the
transparent conductor can fully be suppressed even in a highly
humid environment or the like. Also, the above-mentioned conductive
compound is poor in chemical reactivity to the binder, and thus can
improve the durability of the transparent conductor 15.
Preferably, the conductive polymer is polythiophene. This makes it
possible to form the transparent conductor 15 particularly
excellent in light transmittance and conductivity.
Preferably, the carbon material is a carbon nanotube. Carbon
nanotubes have a large aspect ratio in general, and thus are
advantageous in that they can bring the conductive particles 11
into electric contact with each other.
Preferably, the compounding amount of the conductive compound is 2
to 10 parts by mass with respect to 100 parts by mass in total of
the conductive particles 11 and conductive compound. When the
compounding amount is less than 2 parts by mass, the electric
compensation is harder to attain sufficiently than in the case
where the compounding amount falls within the range mentioned
above. When the compounding amount exceeds 10 parts by mass, the
light transmittance tends to become lower than in the case where
the compounding amount falls within the range mentioned above.
Preferably, the colloid of the conductive compound has a diameter
of 5 nm to 50 nm. When the size of the colloid is 5 nm or less, the
mechanical strength of the transparent conductor tends to become
lower than in the case where the colloid form falls within the
range mentioned above. When the size of the colloid exceeds 50 nm,
the light transmittance tends to become lower than in the case
where the colloid size falls within the range mentioned above.
However, the object of the present invention is achievable even
when the size of the colloid is outside of the above-mentioned
range.
Filler
The transparent conductor 15 may contain a filler. This allows the
binder layer 13 to maintain its morphology when a soft binder 12 is
used for the binder layer 13.
Though not restricted in particular, organic fillers such as
aramide, polystyrene beads, and acrylic beads; inorganic fillers
such as silica, glass, alumina, zirconia, titania, ITO, tin oxide,
and zinc oxide; and the like can be used as the filler.
Preferably used among them are inorganic fillers such as silica,
glass, ITO, tin oxide, and zinc oxide. When the inorganic fillers
are used, the transparent conductor 15 in accordance with this
embodiment exhibits a high transparency.
More preferably used among the inorganic fillers are ITO, tin
oxide, and zinc oxide. In this case, the inorganic fillers
themselves exhibit conductivity, whereby the electric compensation
of the resulting transparent conductor can be made more reliable.
Namely, even when a crack or the like occurs in the transparent
conductor so that the conductive particles 11 are out of contact
with each other, conduction can be achieved through the inorganic
fillers. This can restrain the transparent conductor 15 from
raising its electric resistance value. The conductive inorganic
fillers can be doped with one or a plurality of kinds of elements
in order to improve the conductivity.
Preferably, the compounding amount of the filler is 0. 1 to 70
parts by mass with respect to 100 parts by mass in total of the
binder 12, conductive particles 11, and filler. When the
compounding amount is less than 0.1 part by mass, the morphology
maintaining effect is harder to attain than in the case where the
compounding amount falls within the range mentioned above. When the
compounding amount exceeds 70 parts by mass, optical properties
tend to become lower than in the case where the compounding amount
falls within the range mentioned above.
Preferably, the filler has a particle size of 5 to 100 nm. When the
particle size is 5 nm or less, it tends to become harder to
disperse the filler uniformly into the binder layer 13 than in the
case where the particle size falls within the range mentioned
above. When the particle size exceeds 100 nm, optical properties
tend to become lower than in the case where the particle size falls
within the range mentioned above.
The transparent conductor 15 may further contain additives as
necessary. Examples of the additives include surface-treating
agents, crosslinking agents, photopolymerization initiators, fire
retardants, UV-absorbing agents, colorants, and plasticizers in
addition to the fluorine coating agent and conductive compound
mentioned above.
EXAMPLES
In the following, the present invention will be explained more
specifically with reference to examples, which do not restrict the
present invention.
Making of Conductive Particles
An aqueous solution dissolving 19.9 g of indium chloride
tetrahydrate (manufactured by Kanto Chemical Co., Inc.) and 2.6 g
of stannic chloride (manufactured by Kanto Chemical Co., Inc.) into
980 g of water and a 10-fold water dilution of aqueous ammonia
(manufactured by Kanto Chemical Co., Inc.) were mixed while being
prepared, so as to produce a white precipitate (coprecipitate).
The liquid containing thus produced precipitate was subjected to
solid-liquid separation by a centrifuge, so as to yield a solid.
The solid was put into 1,000 g of water, dispersed by a
homogenizer, and then subjected to solid-liquid separation by the
centrifuge. After performing five sets of dispersion and
solid-liquid separation, the solid was dried, and then was heated
for 1 hour at 600.degree. C. in a nitrogen atmosphere, so as to
yield ITO powder (conductive particles).
Example 1
In a rectangular film. of polyethylene terephthalate (PET) having a
size of 10 cm.times.30 cm (as a support with a thickness of 100
.mu.m; manufactured by Teijin Ltd.) whose one surface was coated
with polyurethane, one end of the surface not coated with
polyurethane was attached to a glass substrate with a double-sided
adhesive tape, so as to secure the support made of the PET film
onto the glass substrate.
Subsequently, 690 parts by mass of thus obtained ITO powder (having
an average particle size of 30 nm) and 2,310 parts by mass of
ethanol (manufactured by Kanto Chemical Co., Inc.) were mixed and
stirred by a mixer, so as to yield a first mixed liquid. The first
mixed liquid was put into a bead mill pulverizer (manufactured by
Kotobuki Industries Co., Ltd.). Then, using 100-.mu.m beads,
pulverization was performed for 180 minutes, so as to pulverize the
ITO powder. The particle size distribution of the ITO power in the
resulting first mixed liquid was measured by using a measuring
instrument, Microtrac UPA. As a result, the average particle size
D50=60 nm. The maximum particle size D100=100 nm. The ratio of
particles having a particle size of 100 nm or greater was 0.15% in
the ITO powder.
The first mixed liquid was applied by bar coating onto the support
and dried. Thereafter, the support coated with the first mixed
liquid was peeled off from the glass substrate. A PET film (having
a thickness of 50 .mu.m; manufactured by Teijin Ltd.) was overlaid
on the surface of the support coated with the first mixed liquid,
and a pressure was applied thereto with a roll press having a width
of 150 mm at a roll pressure of 10 MPa and a feeding rate of 5
m/min. Then, the PET film was peeled off, so as to yield an ITO
powder film on the support. The thickness of thus obtained ITO film
was 1 .mu.m.
On the other hand, 20 parts by mass of ethoxylated bisphenol A
diacrylate (product name: A-BPE-20 manufactured by Shin-Nakamura
Chemical Co., Ltd.), 35 parts by mass of polyethylene glycol
dimethacrylate (product name: 14G manufactured by Shin-Nakamura
Chemical Co., Ltd.), 25 parts by mass of 2-hydroxy-3-phenoxypropyl
acrylate (product name: 702A manufactured by Shin-Nakamura Chemical
Co., Ltd.), 10 parts by mass of a urethane-modified acrylate
(product name: UA-512 manufactured by Shin-Nakamura Chemical Co.,
Ltd.), 10 parts by mass of an acrylic polymer (with an average
molecular weight of about 50,000, having 50 acryloyl groups and 25
triethoxysilane groups on average per molecule), and 1 part by mass
of a photopolymerization initiator (ESACURE ONE manufactured by
Lamberti S.p.A.) were mixed in 50 parts by mass of
methylethylketone (MEK manufactured by Kanto Chemical Co., Inc.),
so as to yield a second mixed liquid.
Then, the second mixed liquid was applied by bar coating onto the
ITO film such that the thickness after curing became 3 .mu.m. After
the resulting product was left for 5 minutes under reduced pressure
at normal temperature, the surface coated with the second mixed
liquid and the PET film (support) were attached together in the
air, and photopolymerization was effected from the support side.
Its condition was such that the integrated illuminance was 4.0
J/cm.sup.2 in the wavelength range of 300 nm to 390 nm by using a
high-pressure mercury lamp as a light source.
Then, the support was separated, so as to yield a transparent
conductive film.
Example 2
A transparent conductive film was obtained as in Example 1 except
that the ITO powder used in Example 1 was pulverized for 180
minutes by using 30-.mu.m beads. Here, the average particle size
D50=43 nm. The maximum particle size D100=80 nm. Namely, the ratio
of particles having a particle size of 100 nm or greater was 0% in
the ITO powder.
Example 3
A transparent conductive film was obtained as in Example 1 except
that the ITO powder used in Example 1 was pulverized for 120
minutes by using 50-.mu.m beads. Here, the average particle size
D50=58 nm. The maximum particle size D100=96 nm. Namely, the ratio
of particles having a particle size of 100 nm or greater was 0% in
the ITO powder.
Example 4
A transparent conductive film was obtained as in Example 1 except
that the ITO powder used in Example 1 was pulverized for 180
minutes by using 50-.mu.m beads. Here, the average particle size
D50=45 nm. The maximum particle size D100=96 nm. Namely, the ratio
of particles having a particle size of 100 nm or greater was 0% in
the ITO powder.
Comparative Example 1
A transparent conductive film was obtained as in Example 1 except
that the ITO powder used in Example 1 was pulverized for 60 minutes
by using 50-.mu.m beads. Here, the average particle size D50=65 nm.
The maximum particle size D100=120 nm. The ratio of particles
having a particle size of 100 nm or greater was 2.15% in the ITO
powder.
Comparative Example 2
A transparent conductive film was obtained as in Example 1 except
that the ITO powder used in Example 1 was pulverized for 120
minutes by using 100-.mu.m beads. Here, the average particle size
D50=70 nm. The maximum particle size D100=100 nm. The ratio of
particles having a particle size of 100 nm or greater was 0.24% in
the ITO powder.
[Evaluation Method]
Optical Properties
Each of the transparent conductive films obtained by Examples 1 to
4 and Comparative Examples 1 to 2 was cut into a 50-mm square, and
the total light transmittance and haze value were measured by a
turbidimeter (NDH2000 manufactured by Nippon Denshoku Industries
Co., Ltd.) at a predetermined measurement point in the ITO surface.
Table 1 shows thus obtained results.
Electric Properties
In the following manner, electric resistance was evaluated in each
of the transparent conductive films obtained by Examples 1 to 4 and
Comparative Examples 1 to 2. Namely, each of the transparent
conductive film obtained as mentioned above was cut into a 50-mm
square, and the surface electric resistance value was measured by a
4-terminal, 4-probe surface resistivity meter (MCP-T600
manufactured by Mitsubishi Chemical Corporation) at a predetermined
measurement point in the ITO surface. Table 1 shows thus obtained
results.
TABLE-US-00001 SURFACE TOTAL RESISTANCE LIGHT VALUE TRANSMITTANCE
HAZE k.OMEGA./.quadrature. % VALUE % EXAMPLE 1 3.45 89.2 2.2
EXAMPLE 2 3.57 90.2 1.6 EXAMPLE 3 3.62 89.4 2.1 EXAMPLE 4 3.24 89.7
1.9 COMPARATIVE 2.93 86.4 5.1 EXAMPLE 1 COMPARATIVE 3.16 86.9 4.5
EXAMPLE 2
As Table 1 clearly shows, Examples 1 to 4 were found to be better
in total light transmittance and haze value than Comparative
Examples 1 to 2. The foregoing results have verified that the
transparent conductor of the present invention can provide a
transparent conductor and a transparent conductive film which are
excellent in light transmittance and haze value.
* * * * *